My understanding is that if you call when you see the item back in stock, they will give you the sale price if you had it cancelled during the sale… which I guess is (technically) different than you just buying it and then calling after the fact to request a price adjustment - could that be it?
This would be similar to price-matching, ie, you have to call and ask them to sell it to you at the matched price, you can’t just shop and buy things and then call them afterward to request that they match the price.
I’m just guessing, though! I definitely agree that it depends on who helps you too, which is really lame.